• Volume 117, Issue 5

      October 2008,   pages  537-645

    • The High Deccan duricrusts of India and their significance for the ‘laterite’ issue

      Cliff D Ollier Hetu C Sheth

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      In the Deccan region of western India ferricrete duricrusts,usually described as laterites,cap some basalt summits east of the Western Ghats escarpment,basalts of the low-lying Konkan Plain to its west,as well as some sizeable isolated basalt plateaus rising from the Plain. The duricrusts are iron-cemented saprolite with vermiform hollows,but apart from that have little in common with the common descriptions of laterite.The classical laterite profile is not present.In particular there are no pisolitic concretions,no or minimal development of con-cretionary crust,and the pallid zone,commonly assumed to be typical of laterites,is absent. A relatively thin,non-indurated saprolite usually lies between the duricrust and fresh basalt.The duricrust resembles the classical laterite of Angadippuram in Kerala (southwestern India),but is much harder.The High Deccan duricrusts capping the basalt summits in the Western Ghats have been interpreted as residuals from a continuous (but now largely destroyed)laterite blanket that represents in situ transformation of the uppermost lavas,and thereby as marking the original top of the lava pile.But the unusual pattern of the duricrusts on the map and other evidence suggest instead that the duricrusts formed along a palaeoriver system,and are now in inverted relief.The two interpretations lead to different tectonic histories.Duricrust formation involved lateral material input besides vertical elemental exchange.We may have reached the stage when the very concepts of laterite and lateritization are hindering progress in regolith research.

    • Comparing groundwater recharge and base flow in the Bukmoongol small-forested watershed, Korea

      E A Combalicer S H Lee S Ahn D Y Kim S Im

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      Groundwater recharge and base flow using different investigated methods are simulated in the 15-ha Bukmoongol small-forested watershed located at the southern part of Korea.The WHAT system, PART,RORA,PULSE,BFI,and RAP software are used to estimate groundwater recharge or base flow and base flow index from the measured stream flow.Results show that about 15 –31 per cent of annual rainfall might be contributed for base flow.The watershed groundwater recharge proportions are computed to about 10 –21 per cent during the wet period and 23 –32 per cent for the remainder periods.Mean annual base flow indices vary from 0.25 to 0.76 estimated using different methods. However,the study found out that all methods were significantly correlated with each other.The similarity of various methods is expressed as a weighted relationship provided by the matrix product from the principal component analysis.Overall,the BFI and WHAT software appeared consistent in estimating recharge or base flow,and base flow index under Korea ’s conditions.The case study recommends the application of different models to other watersheds as well as in low-lying areas where most observation groundwater wells are located with available stream flow data.

    • Surface energy balance of seasonal snow cover for snow-melt estimation in N–W Himalaya

      Prem Datt P K Srivastava P S Negi P K Satyawali

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      This study describes time series analysis of snow-melt,radiation data and energy balance for a seasonal snow cover at Dhundi field station of SASE,which lies in Pir Panjal range of the N –W Himalaya,for a winter season from 13 January to 12 April 2005.The analysis shows that mean snow surface temperature remains very close to the melting temperature of snow.It was found close to -1°C for the complete observational period which makes the snow pack at Dhundi moist from its beginning.The average air temperature over this period was found to be 3.5°C with hourly average variation from -5.5°C to 13°C. The snow surface at this station received a mean short wave radiation of 430 W m−2, out of which 298 W m−2 was re flected back by the snow surface with mean albedo value of 0.70. The high average temperature and more absorption of solar radiation resulted in higher thermal state of the snowpack which was further responsible for faster and higher densification of the snowpack. Net radiation energy was the major component of surface energy budget with a mean value of 83 W m−2. Bulk transfer model was used to calculate turbulent fluxes. The net energy was utilized for satisfying cold content and snow-melt by using measured snow surface temperature and density of snow pack. The mean square error between calculated and measured daily snow-melt was found to be approximately 6.6 mm of water equivalent.

    • Mountain range specific analog weather forecast model for northwest Himalaya in India

      D Singh A Ganju

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      Mountain range specific analog weather forecast model is developed utilizing surface weather observations of reference stations in each mountain range in northwest Himalaya (NW-Himalaya).The model searches past similar cases from historical dataset of reference observatory in each mountain range based on current situation.The searched past similar cases of each mountain range are used to draw weather forecast for that mountain range in operational weather forecasting mode, three days in advance.The developed analog weather forecast model is tested with the independent dataset of more than 717 days (542 days for Pir Panjal range in HP)of the past 4 winters (2003 –2004 to 2006 –2007).Independent test results are reasonably good and suggest that there is some possibility of forecasting weather in operational weather forecasting mode employing analog method over different mountain ranges in NW-Himalaya.Significant difference in overall accuracy of the model is found for prediction of snow day and no-snow day over different mountain ranges, when weather is predicted under snow day and no-snow day weather forecast categories respectively.In the same mountain range,signi ficant difference is also found in overall accuracy of the model for prediction of snow day and no-snow day for different areas.This can be attributed to their geographical position and topographical differences.The analog weather forecast model performs better than persistence and climatological forecast for day-1 predictions for all the mountain ranges except Karakoram range in NW-Himalaya.The developed analog weather forecast model may help as a guidance tool for forecasting weather in operational weather forecasting mode in different mountain ranges in NW-Himalaya.

    • The WRF model performance for the simulation of heavy precipitating events over Ahmedabad during August 2006

      S K Deb T P Srivastava C M Kishtawal

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      The summer monsoon season of the year 2006 was highlighted by an unprecedented number of monsoon lows over the central and the western parts of India,particularly giving widespread rainfall over Gujarat and Rajasthan.Ahmedabad had received 540.2 mm of rainfall in the month of August 2006 against the climatological mean of 219.8 mm.The two spells of very heavy rainfall of 108.4 mm and 97.7 mm were recorded on 8 and 12 August 2006 respectively.Due to meteorological complexities involved in replicating the rainfall occurrences over a region,the Weather Research and Forecast (WRF –ARW version)modeling system with two different cumulus schemes in a nested con figuration is chosen for simulating these events.The spatial distributions of large-scale circulation and moisture fields have been simulated reasonably well in this model,though there are some spatial biases in the simulated rainfall pattern.The rainfall amount over Ahmedabad has been underestimated by both the cumulus parameterization schemes.The quantitative validation of the simulated rainfall is done by calculating the categorical skill scores like frequency bias,threat scores (TS)and equitable threat scores (ETS).In this case the KF scheme has outperformed the GD scheme for the low precipitation threshold.

    • Skills of different mesoscale models over Indian region during monsoon season: Forecast errors

      Someshwar Das Raghavendra Ashrit Gopal Raman Iyengar Saji Mohandas M Das Gupta John P George E N Rajagopal Surya Kanti Dutta

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      Performance of four mesoscale models namely,the MM5,ETA,RSM and WRF,run at NCMRWF for short range weather forecasting has been examined during monsoon-2006.Evaluation is carried out based upon comparisons between observations and day-1 and day-3 forecasts of wind,temperature,specific humidity,geopotential height,rainfall,systematic errors,root mean square errors and specific events like the monsoon depressions.

      It is very difficult to address the question of which model performs best over the Indian region? An honest answer is ‘none ’.Perhaps an ensemble approach would be the best.However, if we must make a final verdict,it can be stated that in general,(i)the WRF is able to produce best All India rainfall prediction compared to observations in the day-1 forecast and,the MM5 is able to produce best All India rainfall forecasts in day-3,but ETA and RSM are able to depict the best distribution of rainfall maxima along the west coast of India,(ii)the MM5 is able to produce least RMSE of wind and geopotential fields at most of the time,and (iii)the RSM is able to produce least errors in the day-1 forecasts of the tracks,while the ETA model produces least errors in the day-3 forecasts.

    • Variational method for objective analysis of scalar variable and its derivative

      S G Narkhedkar S K Sinha

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      In this study real time data have been used to compare the standard and triangle method by performing the objective analysis of mean sea level pressure.In the standard method,derivative fields are obtained from the grid point data using finite difference scheme whereas in the triangle method,a set of non-overlapping triangles are formed from the observations and the scalar and the spatial derivatives are computed directly at the centroid of each of the non-overlapping triangles.These scalars and their derivatives are then mapped to uniform grids by using the standard method.It has been found that objectively analysed scalar field obtained using standard method is superior to the scalar field derived by the triangle method,whereas the derivative fields produced by triangle method are superior to the derivative fields produced using standard method. A variational objective analysis scheme has been developed and an experiment has been carried out with depression case of June (11 –15)2004.It is found that the new scheme (variational)is able to extract the better parts of both triangle and standard methods.The results of this study will be useful in carrying out diagnostic calculations that involve derivative estimates.

    • Tree-ring analysis of teak (Tectona grandis L.F.) in central India and its relationship with rainfall and moisture index

      Somaru Ram H P Borgaonkar A B Sikder

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      Tree-ring-width index chronologies of teak (Tectona grandis L.F.)from three sites in central India have been studied for their dendroclimatic potential.The existence of good correlation among the three site chronologies indicates the influence of common forcing factor to the tree growth of the region.Tree growth and climate relationship based on correlation analysis revealed the important contribution of moisture index and rainfall rather than the direct in fluence of the temperature on tree growth during different seasons.Significant positive relationship of moisture index and rainfall during the monsoon months as well as on the annual scale with tree-ring width variations over the region indicates the important role of moisture availability at the root zone.The results suggest that the teak tree-ring chronologies can be used as high resolution proxy for past precipitation and moisture level in the environment.

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